The present invention relates to an automatic control system in which an input signal or a control circuit is selected in accordance with an operation mode, or more in particular to an automatic control system suitable for avoiding the phenomenon of jump of an output amount in switching the operation mode.
JP-A No. 46-22409, for example, discloses an exclusive control circuit of proportional operation type for automatically controlling an output terminal in accordance with a given condition amount and a manual exclusive control circuit for manually controlling an output terminal, which control circuits are switched in accordance with the operation mode.
Both of the exclusive control circuits disclosed in this conventional system are configured of a simple element of proportional operation or an element of operation of first-order lag.
The disclosed well-known system has not any exclusive control circuits of P (proportional operation)+I (integral operation) type or I+D (differential operation) type covered by the present invention. Specifically, in the case where operation elements such as a P operation element or D operation element in which the signal on output side changes in jump with the change in the signal on input side by switching are arranged in parallel (with an input shared to affect a change in the output terminals of the two operation elements), the amount of instantaneous output change by switching of the operation mode of the P operation element or D operation element is determined by the gain of the P operation element or D operation element respectively, while the signal switching rate on the input side is predetermined, so that the signal on the output side changes in jump, thereby making smooth switching impossible when the gain of the P operation element or the D operation element is comparatively great.